The present invention relates to a method and kit useful for determining the amount of a ligand in a liquid test sample.
Heterogeneous immunoassays for detection of a ligand in a liquid test sample have used a variety of methods to separate antigen complexed with antibody from free antigen. Some of these methods exploit physicochemical properties of the antigen, such as chemical solubility, molecular size, adsorption properties and electrophoretic mobility, whereas others employ immunological techniques in which an antibody which specifically binds the ligand-specific antibody (separation antibody) is used. Several known methods are based on the attachment of the anti-antigen antibody or the antigen itself to a solid phase such as polystyrene, the separation of components being effected by washing steps.
Examples of the variety of such immunoassays are found in, e.g., U.S. Pat. Nos. 4,228,237, 3,879,262, 4,021,534, 4,273,756, 4,098,876, 4,230,683, 4,048,298, 4,243,749, 4,343,896, 4,315,907, 4,332,783, 4,320,109, 4,298,685, 4,185,084, 4,312,944, to cite just a few typical examples. The disclosures of the foregoing patents are hereby incorporated herein by reference in their entireties. Although all of these methods are useful, each suffers from certain limitations, such as the need for purified antigen, the need to attach the antigen to a solid phase, the need for the antigen to have certain physicochemical properties, the use of multiple washing and incubating steps, and the like.
A need therefore continues to exist for a method and kit for immunoassays which avoids these disadvantages.